This paper presents technical results on the developmental work of six (6) kinds of direct injection, high output diesel engines with cylinder bores from 105 mm to 185 mm.The use of the swirl type combustion system can reduce the load on fuel injection equipments. The swirl ratio for the highly supercharged engine must be set at a higher level to compensate for damping of the swirl due to the valve recess, as compared with natural aspirated engines of the same size. As a result, the engine becomes less sensitive to the changes of the swirl ratio and injection timing. With an increase in cylinder bore, the optimum swirl ratio becomes lower, the contour of the combustion chamber has to be changed from the deep to the shallow type, and the number of fuel injection nozzle holes increases for optimum operation. Consequently, the swirl type combustion system is more advantageous under 180 mm cylinder bore.